In the case of making various types of analyses on sample gas, the sample gas is introduced into a cell where measurements are made, and the analyses by various types of analysis parts are made on the sample gas in the cell (see JP 2001-159587). For example, in the case of measuring the concentration of component gas contained in the sample gas on the basis of absorbance, the measurement is made by making a laser beam incident into the cell, and detecting the laser beam that returns outside of the cell after repetitive reflection by a multiple reflection mirror arranged inside the cell.
In such measurement, if dirt adheres to an object having a gas contact surface contacted by the sample gas in the cell, such as the multiple reflection mirror or a cell inner wall surface, due to a component contained in the sample gas, analysis accuracy is spoiled. To overcome this, there is a device that is adapted to, by arranging a gas port toward a predetermined region of the gas contact surface that influences the analysis accuracy, and connecting the gas port to a predetermined purge gas source through a piping mechanism, blow purge gas from the gas port toward the gas contact surface to remove the dirt on the gas contact surface.
However, if a configuration for cleaning the gas contact surface as described above is added, there may occur a problem at a time other than the time of the gas purging for cleaning. Specifically, in the case of not introducing the purge gas, such as at the time of introducing or analyzing the sample gas, the sample gas intrudes from the gas port into the piping mechanism due to an effect of diffusion or the like, and therefore the sample gas is accumulated in dead volume inside the piping mechanism. If the sample gas accumulated in the piping mechanism returns into the cell at the time of the analysis for some reason, a parameter of the sample gas currently present in the cell, such as concentration, is changed, and as a result, accurate measurement may be prevented. In particular, if adsorptive gas such as NH3 is contained in the sample gas, the adsorptive gas adheres to an inner surface of the piping mechanism to accumulate much more gas, and therefore a measurement error is likely to increase.